Composition and process for reducing the adhesive nature of ethylene/alpha-olefins copolymers

ABSTRACT

The process, which makes it possible to reduce the adhesive nature of a partially crystalline copolymer (E) of ethylene and at least one alpha-olefin with a density of between 0.865 and 0.900 approximately, and to increase its resistance to crushing, consists in mixing closely said ethylene copolymer with at least one non-atactic propylene polymer (P) with a fluidity index (measured according to the ASTM D 1238 standard, condition L) between 35 and 200 dg/min. approximately, in a proportion of between 22 to 50 parts by weight approximately for 100 parts by weight of ethylene copolymer.

The present invention relates to a process for reducing the adhesivenature and increasing the crushing resistance of partially crystallineethylene/alpha-olefins copolymers of very low density, and to non-tackyand crushing-resistant compositions of such copolymers and to a processfor preparing the said compositions.

Copolymers of ethylene and of at least one alpha-olefin exhibit anadhesive nature which is proportionately more accentuated the highertheir alpha-olefin content. In terms of density, it can be said that theadhesiveness appears when their density is lower than 0.900.Ethylene/alpha-olefins copolymers with a density lower than 0.890 aregenerally packaged in the form of pellets, granules, blocks or loaves.Their adhesive nature does not present any special problems when theyare in the form of blocks or loaves. On the contrary, when they arepackaged in the form of small-sized pellets or granules (for exampleapproximately 1 to 5 mm) it is difficult to convey them and to storethem in this state, that is to say to avoid their setting solid againafter a prolonged storage period, because they exhibit a marked tendencyto agglomerate, forming compact blocks. Various means which have beenproposed previously to solve this type of problem in the case of variousethylenic elastomers, such as coating the surface of the granules with asilicone oil or with a nonionic surface-active agent such as a copolymerof propylene oxide and ethylene oxide are not wholly satisfactorybecause, while they reduce the adhesiveness considerably at the time ofthe treatment, consequently permitting a substantially correctgranulation, their effect decreases with time. Furthermore, granulestreated with silicone oils or with copolymers of ethylene oxide andpropylene oxide do not withstand crushing; after a prolonged period ofstorage under stress (either the weight of the granules on others in asack, or the weight of the upper sacks on those of the first layer instorage on a pallet) it is found that the granules tend to flatten, toagglomerate and to form a compact mass which is difficult to handle.

Furthermore, Patent FR-A-2,093,589 describes mixtures of crystalline(co)polymers of alpha-monoolefins and of an amorphous ethylene-propyleneor ethylene-propylene-diene rubber, the quantity of the crystalline(co)polymer being from 1 to 30 parts per 100 parts by weight of therubber. According to the examples in this document an atacticpolypropylene or a polypropylene with a melt index equal to 3 may beused as crystalline (co)polymer. The amorphous rubber employed has aMooney viscosity of between 20 and 120.

For its part, Patent EP-A-037,453 describes a mixture comprising anethylene-propylene polymer normally subject to flow at room temperatureand under storage conditions, and a sufficient quantity (preferably upto 20% by weight of the polymer) of polypropylene to reduce thecold-flow. The ethylene-propylene polymer in question has a Mooneyviscosity of 10 to 100 and contains from 40 to 60 mol % of ethylene. Thechosen polypropylene preferably has a melt index of 0.5 to 30 dg/min,measured at 230° C. under 2.16 kg.

The solutions recommended by the last two documents referred to, whichare suitable for elastomers which are amorphous in most cases,exhibiting a Mooney viscosity and generally having a density lower than0.86, are not suitable for partially crystalline ethylene/alpha-olefincopolymers exhibiting no Mooney viscosity and having a density ofapproximately between 0.865 and 0.900. In fact, the addition of anatactic polypropylene or of an isotactic polypropylene of low melt indexto these, in the recommended proportions, does not allow a significantreduction in the adhesiveness and increase the crushing resistance.

The present invention proposes to solve this problem by providing aprocess which, simultaneously, makes it possible to reduce the adhesivenature and to increase the crushing resistance of partially crystallinecopolymers of ethylene and of alpha-olefins with a density ofapproximately between 0.865 and 0.900.

A first subject of the present invention consists of a process making itpossible to decrease the adhesive nature and to increase the crushingresistance of a partially crystalline copolymer (E) of ethylene and ofat least one alpha-olefin, having a density of approximately between0.865 and 0.900, characterised in that it consists in intimatelyblending the said ethylene copolymer with at least one nonatacticpropylene polymer (P) having a melt index (measured according to ASTMstandard D 1238, condition L) of approximately between 35 and 200dg/min, in a proportion ranging approximately from 22 up to 50 parts byweight per 100 parts by weight of ethylene copolymer.

The partially crystalline ethylene copolymer generally comprisesapproximately from 6 to 23 mol % of at least one alpha-olefin whichadvantageously has from 3 to 8 carbon atoms, preferably propylene or1-butene, and preferably has a degree of crystallinity (measured byx-ray diffraction) of at least 1%. Its melt index is generally between0.1 and 100 dg/min, preferably between 0.3 and 15 dg/min. Examples ofsuch copolymers are especially:

the polyolefin rubbers marketed by the Mitsui company under thetrademark Tafmer®, consisting of copolymers of 78 to 92 mol % ofethylene and of 8 to 22 mol % of an alpha-olefin chosen from propyleneand 1-butene, having a density of 0.860 to 0.890, having a degree ofresidual crystallinity of 1 to 14%, a crystalline melting temperature Jof 75° C., which have an average geometric molecular weight of 60 to 120kg/mole and a polydispersity index of between 2.2 and 2.7;

polyolefin rubbers consisting of ethylene/propylene and/or 1-butenecopolymers having a melt index of approximately between 0.3 and 15dg/min and a density of approximately between 0.865 and 0.885,comprising from 77 to 91 mol % of units derived from ethylene and from 9to 23 mol % of units derived from propylene and/or from 1-butene, andwhich have a crystalline melting temperature J of approximately between100 and 125° C. This polyolefin rubber can be subsidiarily characterisedby at least one of the following features:

a polydispersity index of approximately between 3.5 and 15, preferablyapproximately between 4 and 8,

an average geometric molecular weight (defined as shown below) ofapproximately between 35 and 70 kg/mole,

a relationship between the density d and the content x (expressed in mol%) of units derived from propylene and from 1-butene, which is expressedby the double equation:

    0.9084≦d+0.002 x ≦0.918

a degree of residual crystallinity (determined according to the methoddescribed below) of approximately between 3 and 15%.

The crystalline melting temperature J means the temperature determinedat the maximum of the melting curve after crystallisation obtained bysubjecting the copolymer sample to the following three-stage process:

melting at the rate of 8° C. per minute from 10° C. up to 150° C., then

crystallisation at the rate of 8° C. per minute from 150° C. down to 10°C., then again

melting at the rate of 8° C. per minute from 10° C. up to 150° C.

The degree of residual crystallinity is determined by x-ray diffractionon a copolymer sample which has been subjected to cooling at the rate of5° C. per hour from 190° C. down to room temperature. The averagegeometric molecular weight is defined by the mathematical relationship:##EQU1## where W_(i) is the weight fraction of substance of weight M_(i)and N is the number of fractions eluted using gel permeationchromatography. Such a polyolefin rubber can be obtained by a processconsisting in copolymer-rising, at a temperature approximately from 160°C. to 270° C. and at a pressure approximately from 400 to 850 bars, agas stream containing approximately from 18 to 42% by volume of ethyleneand approximately from 58% to 82% by volume of propylene and/or of1-butene, in the presence of a catalyst system of the Ziegler type,comprising, on the one hand, at least one compound of a transition metalfrom groups IVB, VB, VIB and VIII of the Periodic Classification and, onthe other hand, at least one organoaluminium compound and, ifappropriate, in the presence of at least one chain transfer agent. Thecatalyst system may additionally comprise at least one aluminium ormagnesium halide. To obtain the copolymers which have thecharacteristics described above, and in which the molar ratio ( unitsderived from propylene )/( units derived from 1-butene ) exceeds 0.5,the composition of the gas stream subjected to the copolymerization willbe preferably such that the propylene/1-butene volume ratio exceedsapproximately 0.3, depending on the nature of the catalyst systememployed. In fact, the choice of the latter has an influence, known to aperson skilled in the art, on the relative reactivity of ethylene,propylene and 1-butene in the copolymerization and consequently on thetendency to incorporate preferentially units derived from propylene orelse units derived from 1-butene in the macromolecular chain.

A nonatactic propylene poller or copolymer (P) means according to theinvention a propylene homopolymer or copolymer of advantageouslyisotactic structure. It has advantageously a density of approximatelybetween 0.89 and 0.91, an isotacticity index (measured according to ISOstandard 1873) of at least approximately 94% and a degree ofcrystallinity (measured by x-ray diffraction) of at least approximately45%. It may be obtained by polymerisation in the presence ofstereospecific catalysts of the Ziegler type, for example in suspensionin a solvent or in liquid phase. For implementing the invention thepolymer (P) is preferably in the form of powder or granules.Syndiotactic polypropylene may also be employed. The quantity of polymeror copolymer (P) added to the copolymer (E) is proportionately greaterthe lower the density (d) of the copolymer (E), or if it is desired toobtain a more pronounced effect (which may range as far as completedisappearance of the adhesiveness) for a given relative density. Inorder to implement the process according to the invention, this quantityis preferably such that the weight proportion (q) of polymer orcopolymer (P) in the mixture obtained, expressed in %, is related to thedensity (d) by the relationship: q≧600-667 d. It is advantageously atleast 10 parts by weight per 100 parts of copolymer (E).

An intimate blend means that the copolymer (E) forms with the polymer orcopolymer (P), after the latter has been added, a homogeneous mixture inwhich discrete particles of each of the components cannot be discernedmacroscopically. Thus, a simple mixture of granules is not suitable. Oneof the most suitable means for obtaining this intimate blend ismelt-blending of the components followed, if need be, by granulation ofthe composition obtained.

A second subject of the present invention consists of a thermoplasticcomposition comprising, per 100 parts by weight of a partiallycrystalline copolymer (S) of ethylene and of at least one alpha-olefin,having a relative density of approximately between 0.865 and 0.900,approximately from 22 to 50 parts by weight of at least one nonatacticpropylene polymer (P) having a melt index (measured according to ASTMstandard D 1238, condition L) of approximately between 35 and 200dg/min. The definitions of the copolymer (E) and of the polymer orcopolymer (p) which are given above also apply here.

The preferred compositions are those in which the weight proportion (q)of polymer or copolymer (P), expressed in %, is related to the density(d) of the copolymer (E) by the formula:

    q≧600-667 d

The compositions according to the invention may additionally includeusual quantities of antioxidants and/or stabilisers against ultravioletradiation, as well as, where appropriate, up to 100 parts by weight, per100 parts of the composition, of inorganic fillers such as talc, mica,chalk, glass beads, aluminium hydroxide or of organic fillers such assawdust. These fillers may be incorporated by usual means, such as aninternal mixer.

The compositions according to the invention may be converted into films,sheets, plates, rods, profiles, hollow bodies and industrial articlesobtained by injection.

They are advantageously obtained by melt-blending the constituents, forexample in a kneader, an internal mixer or a single-screw or twin-screwextruder with single or twin feed and then, if appropriate, they areconverted into granules. The preferred compositions referred to abovethen produce granules which do not exhibit any adhesive nature and whichhave very good crushing resistance.

Another method of preparation of the compositions according to theinvention is described below.

A third subject of the present invention relates to a particular processfor the preparation of the above compositions, consisting, during thecontinuous preparation of a copolymer (E), in introducing into themolten copolymer (E) the desired quantity of polymer or copolymer (P),also in the molten state. This introduction is possible whatever thepolymerisation conditions. It can be carried out especially as part of aprocess operating at high pressure (300 to 3000 bars) and at hightemperature (160° to 350° C.) in the presence of a catalyst system ofthe Ziegler type. A plant for implementing this process comprises, forexample, a reactor fed with a mixture of ethylene and of comonomers bymeans of a primary compressor followed by a secondary compressor, afirst separator operating at a pressure of approximately 250 bars inwhich the reaction mixture originating from the reactor is allowed toenter and is separated, on the one hand, into copolymer (E) directedtowards a second separator operating at a pressure of approximately 70bars and, on the other hand, into ethylene and comonomers which have notreacted, which are directed towards the intake of the secondarycompressor. The copolymer (E) stream entering the second separator isseparated therein, on the one hand, into copolymer (E) directed towardsa third separator and, on the other hand, into ethylene and comonomerswhich have not reacted towards the intake of the primary compressor. Inthe third separator, also called a hopper, operating at a pressure ofapproximately 1 to 2 bars, the copolymer (E) is degassed and dischargedtowards an extruder and then a granulator.

The introduction of the polymer or copolymer (P) into the plant can takeplace in one of the separators, preferably the third. Advantageously, inorder to ensure the homogeneity of the compositions obtained, theintroduction takes place into the molten copolymer (E) stream, forexample in a separator feed conduit. A twin-entry extruder whose secondentry receives the polymer or copolymer (p) may also be employed as anextruder.

The following examples are intended to illustrate the invention withoutimplying any limitations. Unless stated otherwise, the parts areexpressed by weight.

The following determinations and measurements are carried out on thecopolymers (E) and on the compositions obtained:

-A: adhesiveness, determined by means of a test which consists infilling with granules, to the brim, a frustoconical funnel which has amajor diameter of 15 cm, a conical part 13 cm in height and an orificediameter of 14, 18 or 25 mm, and in then measuring the time (t),expressed in seconds, taken by the granules to flow out completely. Themeasurement is carried out after different storage periods at roomtemperature, in the absence of stress (storage in plastic pouches whichare kept flat).

-CR: crushing resistance, determined by means of a test which consistsin arranging granules filling to the brim a cylindrical polyethylenecontainer 11 cm in height and 12 cm in diameter. A mass of 10 kg (leadcylinder 11 cm in diameter) is then applied to the granules for aspecified period (T). After the chosen time T the time (t') taken by thegranules to empty the cylindrical container completely is measured, whenthe latter is inverted after the applied mass has been taken off.

The results of the measurements appear in the table below.

EXAMPLE 1 (COMPARATIVE)

Granules of lenticular shape (mean diameter: approximately 4 mm, meanheight in the center: approximately 2 mm) of a copolymer (E) of ethylene(78 mol %) propylene (12 mol %) and 1-butene (10 mol %) having a density(measured according to ASTM standard D792) equal to 0.872 and a meltindex (measured according to ASTM standard D 1238 condition E) equal to2.6 dg/min exhibit an adhesiveness such that the said granules,subjected to the corresponding test, require a period of 150 seconds todischarge the funnel which has an orifice diameter of 25 mm, after 6days' storage, After 15 days' storage they can no longer pass throughthis orifice. Their crushing resistance is practically nil: after 1days' application of the mass employed in the corresponding test acompact block is formed, which does not flow.

EXAMPLES 2 AND 3

To the number of parts, which appears in the table below, of thecopolymer (E) of Example 1 there is added, by kneading at 180° C. for aperiod of 6 min, the quantity which is shown in the table below ofpropylene homopolymer (P) having a relative density of 0.90, a meltindex (measured according to ASTM standard D 1238 condition L) equal to45 dg/min, a degree of crystallinity (measured by x-ray diffraction)equal to 65%, marketed under the name Hostalen PPW 1780.

The composition obtained is then converted into granules which have thesame shape and dimensions as in Example 1.

The values obtained for the determination of the adhesiveness (A),expressed as the flow time (t) in seconds of granules from funnels whichhave orifice diameters of 14, 18 and 25 mm, after a storage period of 1,6 and 15 days at room temperature, appear in the table below.

The values obtained for the determination of the crushing resistance(CR), expressed as the time (t') in seconds required by the granules todischarge the cylindrical container after inversion also appear in thetable below.

                                      TABLE                                       __________________________________________________________________________               A (t)                                                                         after   after   after  CR (t')                                                1 day   6 days  15 days                                                                              after                                       Example                                                                            (E)                                                                              (P)                                                                              14 18                                                                              25 14 18                                                                              25 14 18                                                                              25                                                                              1 d.                                                                             6 d.                                                                             15 d.                                 __________________________________________________________________________    1    100                                                                               0 *  * 100                                                                              *  * 150                                                                              *  * * *  *  *                                     2    80 20 113                                                                              30                                                                               10                                                                              150                                                                              42                                                                              10 160                                                                              37                                                                              10                                                                              8  11 10                                    3    70 30  90                                                                              25                                                                               9 155                                                                              35                                                                              10 155                                                                              30                                                                               9                                                                              3  10 10                                    __________________________________________________________________________     *nonflowing block                                                        

We claim:
 1. A process for reducing the adhesive nature and forincreasing the crush resistance of granules of a partially-crystallineethylene/alpha-olefin copolymer of ethylene and at least onealpha-olefin, said ethylene/alpha-olefin copolymer having a densitybetween 0.865 and 0.900 g/cm³ and exhibiting no Mooney viscosity,comprising forming said granules from a composition consistingessentially of an intimate ethylene polymer and propylene polymer blendconsisting of said ethylene/alpha-olefin copolymer and at least onenonatactic propylene polymer having a melt index of between 35 and 200dg/minute in a proportion of from 22 to 50 parts by weight per 100 partsby weight of said ethylene/alpha-olefin copolymer.
 2. A processaccording to claim 1, wherein the weight percentage, q, of the propylenepolymer in the blend is related to the density, d, of theethylene/alpha-olefin copolymer as follows: q≧600-667d.
 3. A processaccording to claim 2, wherein the ethylene/alpha-olefin copolymer has adegree of crystallinity of at least 1%.
 4. A process according to claim1, wherein the ethylene/alpha-olefin copolymer has a degree ofcrystallinity of at least 1%.
 5. A process according to claim 1, whereinthe blend is formed by introducing said propylene polymer in a moltenstate into said ethylene/alpha-olefin copolymer in a molten state duringcontinuous preparation of the ethylene/alpha-olefin copolymer.
 6. Aprocess according to claim 1, wherein the propylene polymer is anisotactic polypropylene polymer having a relative density of between0.89 and 0.91 g/cm³, an isotacticity index of at least 94% and a degreeof crystallinity of at least 45%.
 7. A thermoplastic article formed fromgranules consisting essentially of an intimate ethylene polymer andpropylene polymer blend consisting of 100 parts by weight of apartially-crystalline ethylene/alpha-olefin copolymer of ethylene and atleast one alpha-olefin, said ethylene/alpha-olefin copolymer having adensity between 0.865 and 0.900 g/cm3 and exhibiting no Mooneyviscosity, and from 22 to 50 parts by weight of at least one nonatacticpropylene polymer having a melt index of between 35 and 200 dg/minute.8. A thermoplastic article formed from granules according to claim 7,wherein the weight percentage, q, of the propylene polymer in thegranules is related to the density, d, of the ethylene/alpha-olefincopolymer as follows: q≧600-677d.
 9. A thermoplastic article formed fromgranules according to claim 16 wherein the ethylene/alpha-olefincopolymer has a degree of crystallinity of at least 1%.
 10. Athermoplastic article formed from granules according to claim 16 whereinthe propylene polymer is an isotactic polypropylene polymer having arelative density of between 0.89 and 0.91 g/cm³, an isotacticity indexof at least 94% and a degree of crystallinity of at least 45%.
 11. Athermoplastic article formed from granules according to claim 7 furtherincluding up to 100 parts by weight of at least one filler per 100 partsby weight of the ethylene-alpha olefin copolymer and nonatacticpropylene polymer.
 12. An article formed from granules according toclaim 11, further including an antioxidant.
 13. An article formed fromgranules according to claim 11, further including a stabilizer againstultraviolet radiation.
 14. A thermoplastic article according to claim 7,wherein the article is in the form of a film, sheet, plate, rod,profile, or hollow body.
 15. Granules consisting essentially of anintimate ethylene polymer and propylene polymer blend consisting of 100parts by weight of a partially-crystalline ethylene/alpha-olefincopolymer having a density between 0.865 and 0.900 g/cm³ and exhibits noMooney viscosity, and 22 to 50 parts by weight of at least onenonatactic propylene polymer having a melt index of between 35 and 200dg/minute.
 16. Granules as recited in claim 15 consisting of said blend.17. Granules produced by the process of claim 1 formed into the shape ofan industrial article.